Optoelectronic device comprising three-dimensional diodes

ABSTRACT

An optoelectronic device including a support having a rear surface and a front surface opposite each other, a plurality of nucleation conductive strips forming first polarization electrodes, an intermediate insulating layer covering the nucleation conductive strips, a plurality of diodes, each of which having a first, three-dimensional doped region and a second doped region, and a plurality of top conductive strips forming second polarization electrodes and resting on the intermediate insulating layer, each top conductive strip being disposed in such a way as to be in contact with the second doped regions of a set of diodes of which the first doped regions are in contact with different nucleation conductive strips.

TECHNICAL FIELD

The field of the invention is that of optoelectronic devices comprisingelectroluminescent diodes or photodiodes. The invention is applied inthe field of devices comprising a matrix of electroluminescent diodessuch as lighting devices, display screens, and image projectors, as wellas in the field of devices comprising a matrix of photodiodes such asphotodetectors and sensors.

PRIOR ART

There are optoelectronic devices having a matrix of electroluminescentdiodes suitable for producing lighting devices, display screens, andimage projectors. The document EP2960950 illustrates an example of anoptoelectronic device comprising a matrix of electroluminescent diodes.As shown schematically in FIG. 1, this optoelectronic device A1comprises a plurality of electroluminescent diodes A2, each comprising astack of a p-doped region A11 and an n-doped region A9 separated fromeach other by an active zone A10 from which the majority of the luminousradiation of the diode A2 is generated.

The electroluminescent diodes A2 have a so-called mesa structure, i.e.they are obtained from a stack of semiconductor layers configured toform the n- and p-doped regions A9, A11 and the active zone A10,localized etching being carried out in such a way as to individuallyseparate the electroluminescent diodes A2 from one another. Each diodeA2 comprises an L-shape the sides of which are coated with an insulatinglayer, except in a recess A3 that forms the n-doped region A9. Firstelectrodes A14 rest on the top surface of the p-doped regions A11, andsecond electrodes A6 extend between the diodes A2 and come into contactwith recesses A3 formed by the n-doped regions A9. A display pixel thencomprises the stack of the doped regions A9, A11, the active zone A10,and the first electrode A14, as well as the second electrode A6 adjacentto the stack. A connection structure is assembled to the top surface ofthe matrix of electroluminescent diodes and is designed to be hybridizedto a control integrated circuit.

However, this optoelectronic device has the drawback of requiring a stepof etching the doped semiconductor layers and the active layer in orderto individually separate the diodes. This etching step can cause theformation of structural defects that may degrade the optical and/orelectronic properties of the diodes. Moreover, the ratio of the emittingsurface of each diode to the surface of each pixel is reduced by theneed to form a recess in the n-doped region and by the presence of thesecond electrode that extends between the diodes in such a way as tocome into contact with this recess. This thus reduces the maximumluminous intensity relative to each pixel.

DESCRIPTION OF THE INVENTION

The object of the invention is to at least partially overcome thedrawbacks of the prior art, and more particularly to propose anoptoelectronic device comprising:

-   -   a support that has a rear surface and a front surface opposite        each other;    -   a plurality of nucleation conductive strips that form first        polarization electrodes, distinct from each other and resting on        said front surface, made of an electrically conductive material        suitable for the growth of first doped regions of diodes;    -   an intermediate insulating layer that covers the nucleation        conductive strips and comprises through-openings opening onto        the nucleation conductive strips;    -   a plurality of diodes, each of which has a first        three-dimensional doped region and a second doped region        disposed in such a way as to form a p-n junction, the first        doped regions being in contact with the nucleation conductive        strips through said through-openings and extending along a        longitudinal axis substantially orthogonal to the front surface;    -   a plurality of top conductive strips that form second        polarization electrodes, distinct from each other and resting on        the intermediate insulating layer, each top conductive strip        being disposed in such a way as to be in contact with second        doped regions of a set of diodes of which the first doped        regions are in contact with different nucleation conductive        strips.

Some preferred but not limiting aspects of this optoelectronic deviceare as follows.

The support can comprise an electrically insulating substrate of which atop surface forms said front surface, or can comprise a semiconductor orelectrically conductive layer or substrate, coated with a so-calledbottom insulating layer, one surface of which forms said front surface.

Each nucleation conductive strip can extend longitudinally on the frontsurface, being electrically separated from its neighbors, transversely,by said intermediate insulating layer.

Each top conductive strip can extend longitudinally on the intermediateinsulating layer, being electrically separated from its neighbors,transversely, by a so-called top insulating layer.

The top conductive strips can be made of an at least partiallytransparent conductive material, and can at least partially cover thesecond doped regions.

Each top conductive strip can comprise portions that cover the seconddoped regions of a set of diodes, said so-called covering portions beingconnected to each other by so-called connecting parts resting on theintermediate insulating layer.

The connecting parts of the top conductive strips can be at leastpartially coated with a metal layer.

The optoelectronic device can comprise first connection pads resting onsaid rear surface and electrically connected to the nucleationconductive strips by first openings passing through the support andfilled with a conductive material, and/or can comprise second connectionpads resting on said rear surface and electrically connected to the topconductive strips by second openings passing through the support and theintermediate insulating layer and filled with a conductive material.

The optoelectronic device can comprise a control integrated circuitassembled to the support and electrically connected to the nucleationconductive strips and the top conductive strips, suitable for applying apotential difference, sequentially, to different subsets of diodes, theone or more diodes of a same subset being in contact with a samenucleation conductive strip and a same top conductive strip, the one ormore diodes of different subsets of diodes being in contact withdifferent nucleation conductive strips and/or different top conductivestrips.

At least one diode in contact with a first nucleation conductive stripand a first top conductive strip can be connected in series with atleast one other diode, the latter being in contact with a secondnucleation conductive strip distinct from the first nucleation strip anda second top conductive strip distinct from the first top strip.

The support can be composed of a substrate made of a monocrystallinematerial that forms a top surface, on which rests a so-called bottominsulating layer made of a dielectric material, epitaxially grown fromthe top surface of the substrate and forming an opposing top surface,the nucleation conductive strips being made of a material comprising atransition metal forming a crystalline nucleation material, epitaxiallygrown from the top surface of the bottom insulating layer and forming anucleation surface on which the first doped regions of said diodes arein contact.

The material of the bottom insulating layer can be selected fromaluminum nitride and oxides of aluminum, titanium, hafnium, magnesiumand zirconium, and has a hexagonal, face-centered cubic, or orthorhombiccrystalline structure.

The material of the nucleation conductive strips can be selected fromtitanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium,tantalum and tungsten, or from a nitride or a carbide of titanium,vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalumand tungsten, and has a hexagonal or face-centered cubic crystallinestructure. In a variant, it can be a gallium-nitride-based material, forexample GaN, AlGaN, InGaN, or AlInGaN.

The monocrystalline material of the substrate can be selected from agroup III-V compound, a group II-VI compound, or a group IV element orcompound, and has a hexagonal or face-centered cubic crystallinestructure.

The invention also relates to a method for producing the optoelectronicdevice according to any of the preceding characteristics, comprising astep of epitaxial growth of the nucleation conductive strips bysputtering at a growth temperature between room temperature and 500° C.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, objects, advantages and characteristics of the inventionwill be better understood after reading the following detaileddescription of preferred embodiments thereof, given by way ofnon-limiting example and with reference, except for FIG. 1 describedabove, to the attached drawings, which are as follows:

FIG. 2A is a schematic and partial top view of an optoelectronic deviceaccording to an embodiment wherein a plurality of diodes is in contactwith the nucleation conductive strips and the top conductive strips; andFIGS. 2B and 2C are sectional views, respectively along planes AA andBB, of the optoelectronic device shown in FIG. 2A;

FIGS. 3A and 3B are, respectively exploded and perspective, schematicand partial views of the substrate, the bottom insulating layer, and thenucleation conductive strips (arranged from bottom to top) of anoptoelectronic device according to a preferred embodiment; and FIGS. 3Cand 3D are top views of epitaxial wires on textured nucleation surfaces(FIG. 3C) and on epitaxial nucleation surfaces (FIG. 3D);

FIGS. 4A to 4I show sectional views along plane AA and plane BB ofdifferent steps of a method of implementing an optoelectronic deviceaccording to another embodiment;

FIG. 5 is a schematic and partial top view of an optoelectronic deviceaccording to an embodiment wherein each pixel comprises several diodes;

FIGS. 6A and 6B are cross-sectional schematic and partial views of anoptoelectronic device comprising a routed integrated circuit havingelectrical series interconnections of pixels (FIG. 6A) and of anoptoelectronic device comprising internal electrical interconnectionswith serialized pixels (FIG. 6B).

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the figures and in the remainder of the description, the samereference numbers represent identical or similar elements. Moreover, thedifferent elements are not shown to scale in order to make the figuresclearer. In addition, the different embodiments and variants are notexclusive of one another and can be mutually combined. Unless otherwiseindicated, the terms “substantially”, “approximately”, and “of the orderof” mean “within 10%” or, in the case of angular orientation, “within10°”.

The invention relates to an optoelectronic device comprising diodes, forexample electroluminescent diodes having a three-dimensional shape, eachof which comprises a first doped region and a second doped regiondisposed in such a way as to form a p-n junction. The diodes can beelectroluminescent diodes suitable for emitting luminous radiation orphotodiodes suitable for receiving luminous radiation. Thethree-dimensional shape of the diodes can be such that the diodes have awire, pad, pyramidal, or other shape. The first doped regions of thediodes extend along a longitudinal axis substantially orthogonal to themain plane of the support.

The optoelectronic device comprises first electrodes suitable forbringing the first doped regions of the diodes to a first electricalpotential V1 and second electrodes suitable for bringing the seconddoped regions to a second electrical potential V2. The first electrodesare in the form of nucleation conductive strips, distinct from eachother, on which rest and are in contact the first doped regions. Thesecond electrodes are in the form of so-called top conductive strips,distinct from each other, in contact with the second doped regions.

Here, and for the remainder of the description, a directthree-dimensional reference (X, Y, Z) is defined, wherein the X and Yaxes form a plane parallel to the main plain of the substrate, andwherein the Z axis is oriented substantially orthogonal to the growthsurface of the substrate. In the remainder of the description, the terms“vertical” and “vertically” are understood to be relative to anorientation substantially parallel to the Z axis, and the terms“horizontal” and “horizontally” are understood to be relative to anorientation substantially parallel to the plane (X, Y). In addition, theterms “less” and “greater” are understood to be relative to anincreasing positioning when one moves away from the growth surface ofthe substrate in the direction +Z.

The term conductive strip is understood to refer to a section of asemiconductor or conductive material, deposited in a thin layer, thathas a longitudinal dimension in the plane (X, Y), or a length, greaterthan the transverse dimension in the plane (X, Y), or its width, andthan the dimension of thickness along the Z axis.

Each nucleation conductive strip of index i is in contact with a setD_(i) of several diodes that are in contact with different topconductive strips. Similarly, each top conductive strip of index j is incontact with a set D_(j) of several diodes that are in contact withdifferent nucleation conductive strips. Thus, the one or more diodesthat are in contact with a same nucleation conductive strip of index iand a same top conductive strip of index j form a pixel P of indices i,j.

FIGS. 2A, 2B and 2C are schematic and partial views, from the toprespectively, in cross-section along plane AA and plane BB, of anoptoelectronic device 1 comprising electroluminescent diodes 2 accordingto a first embodiment.

The optoelectronic device 1 comprises:

-   -   a support 3, comprising so-called back 3 a and front 3 b        surfaces opposite each other;    -   a plurality of first electrodes in the form of so-called        nucleation conductive strips 6 _(i), distinct from each other        and resting on said front surface 3 b, made of an electrically        conductive material suitable for the growth of the first doped        regions 9 of diodes 2;    -   an intermediate insulating layer 7 that covers the nucleation        conductive strips 6 _(i) and comprises through-openings 8        opening onto the nucleation conductive strips 6 _(i);    -   a plurality of diodes 2, each of which has a first        three-dimensional doped region 9 and a second doped region 11        disposed in such a way as to form a p-n junction, the first        doped regions 9 being in contact with the nucleation conductive        strips 6 _(i) through said through-openings 8 and extending        along a longitudinal axis Δ substantially orthogonal to the        front surface 3 b;    -   a plurality of second electrodes in the form of so-called top        conductive strips 14 _(j), distinct from each other and resting        on the intermediate insulating layer 7, each top conductive        strip 14 _(j) being disposed in such a way as to be in contact        with second doped regions 11 of a set D_(j) of diodes 2 of which        the first doped regions 9 are in contact with different        nucleation conductive strips 6 _(i).

As discussed in detail below, the one or more diodes 2 in contact with anucleation conductive strip 6 of index i and in contact with a topconductive strip 14 of index j form an emissive pixel P_(ij). Thus, aplurality of emissive pixels P_(ij) is formed by the arrangement of thefirst and second electrodes in several conductive strips distinct fromeach other. In this example, each pixel P_(ij) comprises a single diode,but in a variant can comprise a plurality of diodes. In other words,each nucleation conductive strip 6 _(i) is in contact with a set D_(i)of diodes, distributed in subsets P_(ij) distinct from one another. Eachsubset P_(ij) of diodes of a same nucleation conductive strip 6 _(i) isin contact with a same top conductive strip 14 of index j and forms apixel P_(ij).

The support 3 comprises two surfaces, the so-called front 3 b and rear 3a surfaces, which are opposite each other. It can be a monoblocstructure or be composed of a stack of layers such as a substrate 4 ofthe SOI (silicon on insulator) type. It comprises an electricallyinsulating material at the level of the front surface 3 b. It can thusbe composed, for example, of an insulating monobloc substrate 4 or becomposed of a semiconductor or conductive substrate 4 of which the topsurface is coated with an insulating layer 5.

The material of the substrate 4 can be electrically insulating, such ase.g. an oxide of silicon (such as SiO₂) or of sapphire, or be asemiconductor material selected for example from the group III-Vcompounds comprising at least one element of group III and at least oneelement of group V of the periodic table, the group II-VI compounds, orthe group IV elements or compounds. By way of example, it can besilicon, germanium, or silicon carbide. Preferably, the semiconductormaterial of the substrate 4 is monocrystalline silicon.

The substrate 4 can have a thickness between 50 nm and 1500 μm,depending on whether or not it has been thinned. In this example,wherein the support has been thinned in order to allow resumption ofelectrical contact on the rear surface 3 a, it has a thickness forexample of between 10 μm and 300 μm, preferably between 10 μm and 100μm. In cases where it has not been thinned, particularly when theresumption of contact is carried out on the front surface 3 b, it has athickness between 300 μn and 1500 μm, for example equal to approximately725 μm.

In this example, the support is composed of a semiconductor substrate 4of which the top surface is coated with a so-called bottom insulatinglayer 5 made of a dielectric material. The bottom insulating layer 5provides electrical insulation between the nucleation conductive strips6 _(i) and the substrate 4 when the latter is electrically conductive.The material of the bottom insulating layer 5 can be an oxide of silicon(such as SiO₂) or of aluminum (such as Al₂O₃), a nitride of silicon SiNxor of aluminum AlN, an oxynitride of silicon SiOxNy, or any othersuitable material. The thickness of the bottom insulating layer 5 can bebetween 5 nm and 500 nm, preferably between 10 nm and 100 nm, forexample equal to approximately 30 nm.

In a variant (not shown), the substrate can be omitted and the supportcan then be composed of a deposited layer, for example a reflectinglayer, optionally metallic, allowing the reflection of the incidentluminous radiation emitted by the diodes 2. The steps of omission of thesubstrate and depositing the layer of the support can be carried outafter production of the diodes.

The first polarization electrodes are disposed in such a way as to allowthe application of a first electrical potential V1 _(i) to differentsets of diodes. They take the form of a plurality of nucleationconductive strips 6 _(i) that rest on the front surface 3 b of thesupport, here the top surface of the bottom insulating layer 5. Eachnucleation conductive strip 6 _(i) has a top surface, opposite the frontsurface 3 b of the support, that forms a nucleation surface with whicheach first doped region 9 of the diode 2 is in contact. The nucleationconductive strips 6 _(i) are distinct from each other and can have anelectrical potential V1 _(i), which varies over time, the value of whichcan differ from one strip to the other. They can extend longitudinallyin the plane (X, Y) in a rectilinear or curved manner parallel to oneanother. Each nucleation conductive strip 6 of index i is in contactwith a set D_(i) of diodes at the level of the first doped regions 9thereof, the sets of diodes differing from one nucleation conductivestrip 6 _(i) to the other.

The nucleation conductive strips 6 _(i) are made of an electricallyconductive material suitable for the nucleation and growth of the firstdoped regions 9. This material can be made of gallium nitride GaN or analloy based on gallium nitride, for example an alloy of gallium nitrideand aluminum AlGaN, gallium nitride and indium InGaN, or even galliumnitride, aluminum, and indium AlInGaN. In a variant, the nucleationconductive strips 6 _(i) can be made of a material comprising atransition metal. It can be selected from titanium, vanadium, chromium,zirconium, niobium, molybdenum, hafnium, tantalum and tungsten, or madeof a nitride or a carbide of a transition metal, for example titanium,zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,tantalum, or made of a combination of these compounds. The transitionmetals, as well as their nitrides and carbides, have the advantages ofallowing nucleation of the first doped regions 9 and having anelectrical conductivity close to that of the metals. The nucleationconductive strips 6 _(i) have a width for example of between 5 nm and500 nm, preferably between 10 nm and 100 nm, for example equal toapproximately 30 nm. They have a transverse dimension in the plane (X,Y), or a width, for example, of between 20 nm and 50 μm, preferablybetween 200 nm and 10 μm, and preferably between 800 nm and 5 μm, forexample equal to approximately 1 μm. The nucleation conductive strips 6_(i) are transversely spaced with respect to one another at a distancefor example of between 500 nm and 20 μm, and preferably between 1000 nmand 2000 nm, for example equal to 1500 nm.

The optoelectronic device 1 also comprises a so-called intermediateinsulating layer 7 that covers the front surface 3 b of the support, andcovers in particular the nucleation conductive strips 6 _(i). It forms agrowth mask allowing epitaxial growth of the first doped regions 9 ofthe diodes from through-openings 8 opening locally onto the nucleationsurfaces. Moreover, it extends in such a way as to separate eachnucleation conductive strip 6 _(i), transversely, from its neighbors. Italso plays a role in providing the electrical insulation between thenucleation conductive strips 6 _(i) and the top conductive strips 14_(j). The intermediate insulating layer 7 is made of one or moredielectric materials such as, for example, an oxide of silicon (such asSiO₂) or a nitride of silicon (such as Si₃N₄ or SiN), or even anoxynitride of silicon, an oxide of aluminum (such as Al₂O₃) or an oxideof hafnium (such as HfO₂). The thickness of the intermediate insulatinglayer 7 can be between 5 nm and 500 nm, and preferably between 30 nm and300 nm, for example equal to approximately 100 nm.

Each electroluminescent diode 2 comprises a first doped region 9 ofthree-dimensional shape. In this embodiment, the first doped regions 9have an elongated shape along a longitudinal axis Δ, i.e. in which thelongitudinal dimension along the longitudinal axis Δ is greater than thetransverse dimensions. The first doped regions 9 are then referred to as“wires”, “nanowires”, or “microwires”. The transverse dimensions of thewires 9, i.e. their dimensions in a plane orthogonal to the longitudinalaxis Δ, can be between 10 nm and 10 μm, for example between 100 nm and10 μm, and preferably between 100 nm and 5 μm. The height of the wires9, i.e. their longitudinal dimension along the longitudinal axis Δ, isgreater than the transverse dimensions, for example 2 times, 5 times,and preferably at least 10 times greater. The cross-section of the wires9, in a plane orthogonal to the longitudinal axis Δ, can have differentshapes, for example a circular, oval, polygonal, e.g. triangular,square, rectangular or even hexagonal shape. Here, the diameter isdefined as being a parameter associated with the perimeter of the wireat the level of a cross-section. It can be the diameter of a disk havingthe same surface as the cross-section of the wire. The local diameter isthe diameter of the wire at a given height thereof along thelongitudinal axis Δ. The mean diameter is the mean, for example thearithmetic mean, of the local diameters along the wire or a portionthereof.

Each first doped region 9 extends from the nucleation surface of anucleation conductive strip 6 _(i), along a longitudinal axis Δ orientedsubstantially orthogonal to the plane (X, Y). Each diode 2 alsocomprises an active zone and a second doped region 11. Here, the wire 9forms the core of an electroluminescent diode 2 in a core/shellconfiguration, with the active zone and the second doped region 11covering the lateral edge of a so-called upper portion 13 of the wire 9.The wires 9 comprise a bottom portion 12 that is in contact with thenucleation surfaces and is surrounded by the intermediate insulatinglayer 7. This bottom portion 12 is extended by the top portion 13 thatis located outside the through growth openings 8 and is covered by theactive zone and the second doped region 11.

The wires 9 can be made from a crystalline material epitaxially grownfrom the nucleation surface. The material of the wires 9 predominantlycomprises a first semiconductor compound that can be selected from groupIII-V compounds and in particular from group III-N compounds, groupII-VI compounds, or group IV compounds or elements. By way of example,group III-V compounds can be compounds such as GaN, InGaN, AlGaN, AlN,InN or AlInGaN, or even compounds such as AsGa or InP. Group II-VIcompounds can be CdTe, HgTe, CdHgTe, ZnO, ZnMgO, CdZnO, or CdZnMgO.Group IV elements or compounds can be Si, C, Ge, SiC, SiGe, or GeC. Thewires 9 thus form the first regions of the diodes, and are dopedaccording to a first type of conductivity, here type n. In this example,the wires 9 are made of n-doped GaN, particularly with silicon. Here,they have an average diameter of between 10 nm and 10 μm, for examplebetween 500 nm and 5 μm, and is here substantially equal to 500 nm. Theheight of the wires 9 can be between 100 nm and 100 μm, for examplebetween 500 nm and 50 μm, and is here substantially equal to 5 μm.

The active zone is the region of the diode 2 at the level of which mostof the luminous radiation of the diode is emitted. It can comprise atleast one quantum well made of a semiconductor compound having a bandgap energy less than those of the wire 9 and the second doped region 11.Here, it covers the upper edge and the lateral edge of the wire 9. Itcan comprise a single quantum well or a plurality of quantum wells inthe form of layers or boxes intercalated between barrier layers.Alternatively, the active zone may not comprise a quantum well. It canhave a band gap energy substantially equal to that of the wire 9 and thesecond doped region 11. It can be made of a semiconductor compound thatis not intentionally doped.

The second doped region 11 forms a layer that covers and at leastpartially surrounds the active zone. It is made of a secondsemiconductor compound doped according to a second type of conductivityopposite to the first type, i.e. here of type p. The secondsemiconductor compound can be identical to the first semiconductorcompound of the wire or can comprise the first semiconductor compoundand also one or more additional elements. In this example, the seconddoped region 11 can be p-doped GaN or InGaN, particularly withmagnesium. The thickness of the second doped region 11 can be between 20nm and 500 nm, and can be equal to approximately 150 nm. Of course, thetypes of conductivity of the first and second regions 9, 11 can bereversed.

The second doped region 11 can also comprise an electron blockinginterlayer (not shown) located at the interface with the active zone.Here, the electron blocking layer can be composed of a ternary III-Ncompound, such as AlGaN or AlInN, advantageously p-doped. This makes itpossible to increase the rate of radiative recombinations in the activezone.

The second polarization electrodes 14 _(j) are disposed in such a way asto allow the application of a second electrical potential V2 _(j) todifferent sets of diodes. They take the form of a plurality of so-calledtop conductive strips 14 _(j) that rest on the top surface of theintermediate insulating layer 7. They are distinct from each other andcan have an electrical potential V2 _(j) that varies with time, thevalue of which can differ from one strip to the other. They are alsoelectrically separated from the nucleation conductive strips 6 _(i) bythe intermediate insulating layer 7. They can extend longitudinally inthe plane (X, Y) in a rectilinear or curved manner parallel to oneanother. In this embodiment, each top conductive strip 14 _(j) extendslongitudinally and comprises portions 15 _(j) that cover the seconddoped regions 11 of said diodes 2 that are interconnected by so-calledconnecting parts 16 _(j) extending in a substantially planar manner onthe top surface of the intermediate insulating layer 7.

Each top conductive strip 14 of index j is in contact with a set D_(j)of diodes 2 at the level of the second doped regions 11 thereof, thesets D_(j) of diodes 2 being different from one top conductive strip 14_(j) to the other. The top conductive strips 14 _(j) extend transverselyto the nucleation conductive strips 6 _(i), such that a set D_(i) ofdiodes 2 in contact with a nucleation conductive strip 6 of index i isnot identical to a set D_(j) of diodes 2 in contact with a topconductive strip 14 _(j). The intersection between a set D_(i) of diodes2 of a nucleation conductive strip 6 of index i and a set D_(j) ofdiodes 2 of a top conductive strip 14 of index j forms a pixel P_(ij).

The top conductive strips 14 _(j) are made of an electrically conductivematerial, and when they cover the second doped regions 11, this materialis advantageously transparent to the luminous radiation emitted by thediodes. For example, it can be an indium tin oxide (ITO), or agallium-doped zinc oxide (GZO), or even a material doped with aluminumor indium. The term transparent, or at least partially transparent, isunderstood to refer to a material that transmits at least 50% ofincident light, and preferably at least 80% or even more.

The top conductive strips 14 _(j) have a thickness for example ofbetween 5 nm and 500 nm, preferably between 10 nm and 100 nm, forexample equal to approximately 50 nm. They have a transverse dimensionin the plane (X, Y), or a width, for example, of between 20 nm and 50μm, preferably between 200 nm and 10 μm, preferably between 800 nm and 5μm, for example equal to approximately 1.5 μm. The width is such thateach top conductive strip 14 _(j) is electrically separated from itsneighbors. The length of the top conductive strips 14 _(j) is such thateach top conductive strip 14 _(j) is in contact with the second dopedregions 11 of a set of diodes 2 that are in contact with differentnucleation conductive strips 6 _(i). The top conductive strips 14 _(j)are transversely spaced with respect to one another at a distance forexample of between 1000 nm and 10 μm, preferably between 1000 nm and3000 nm, for example equal to 2500 nm.

In this embodiment, a so-called top insulating layer 18 that is at leastpartially transparent conformally covers the top conductive strips 14_(j) and the top surface of the intermediate insulating layer 7. It canbe made of a dielectric material transparent to the luminous radiationemitted by the diodes, for example, an oxide of silicon (such as SO₂) orof aluminum (such as Al₂O₃), a nitride of silicon SiNx or of aluminumAlN, an oxynitride of silicon SiOxNy, or any other suitable material. Ithas a thickness for example of between 5 nm and 500 nm, preferablybetween 50 nm and 300 nm, for example equal to approximately 100 nm.

In this example, a reflecting layer 19 is present between the diodes 2and rests on the top insulating layer 18, but without covering the wires9. It is made of a material suitable for reflecting the incidentluminous radiation emitted by the diodes 2 toward the exterior of theoptoelectronic device 1 in the direction +Z. The material can be ametal, for example aluminum, silver, gold, copper, or a combinationthereof, or any other suitable material. The reflecting layer 19 has athickness for example of between 10 nm and 2 μm, and preferably between100 nm and 500 nm, for example equal to approximately 200 nm.

In this example, an encapsulation layer 20 covers the diodes. It is madeof a dielectric material at least partially transparent to the luminousradiation emitted by the diodes and can for example be an oxide ofsilicon (such as SiO₂) or of aluminum (such as Al₂O₃), a nitride ofsilicon SiNx or of aluminum AlN, an oxynitride of silicon SiOxNy, or anyother suitable material. The thickness of the encapsulation layer 20 issuch that it covers the diodes, particularly at their peak. It is forexample between 500 nm and 50 μm.

As shown in FIG. 2B, the optoelectronic device 1 also comprises aplurality of first connection pads 21 _(i) each being electricallyconnected to a nucleation conductive strip 6 _(i). The first connectionpads 21 _(i) can be located on the front surface 3 b or on the rearsurface 3 a of the support. In this example, the electrical connectionis carried out on the rear surface 3 a of the support. For this purpose,first through openings 22 _(i) extend between the front 3 b and rear 3 asurfaces of the support, each opening onto a nucleation conductive strip6 _(i). The through openings 22 _(i) are filled with a conductivematerial 23 and are in contact on the one hand with the material of thenucleation conductive strip 6 _(i) and on the other with a firstconnection pad 21 _(i). In order to insulate, if necessary, the materialof the semiconductor or conductive substrate 4, the sides of the throughopenings 22 _(i) are coated with an insulating layer 24. The fillingmaterial 23 and that of the first connection pads 21 _(i) can be copper,gold, aluminum, or any other suitable conductive material.

As shown in FIG. 2C, the optoelectronic device 1 also comprises aplurality of second connection pads 25 _(j), each being electricallyconnected to a top conductive strip 14 _(j). The second connection pads25 _(j) can be located on the front surface 3 b or the rear surface 3 aof the support. In this example, the electrical connection is carriedout on the rear surface 3 a of the support. For this purpose, secondthrough openings 26 _(j) extend between the front 3 b and rear 3 asurfaces of the support, each opening onto a top conductive strip 14_(j). The through openings 26 _(j) are filled with a conductive material23 and are in contact on the one hand with the material of the topconductive strip 14 _(j) and on the other with a second connection pad25 _(j). In order to insulate, if necessary, the conductive material ofthe semiconductor substrate 4, the sides of the through openings 26 _(j)are coated with an insulating layer 24. The filling material 23 and thatof the second connection pads 25 _(j) can be copper, gold, aluminum, orany other suitable conductive material.

An insulating layer 27 can cover the rear surface 3 a of the support insuch a way as to electrically insulate the first and second connectionpads 21 _(i) and 25 _(j) with respect to the material of the substrate4.

The optoelectronic device 1 comprises a control integrated circuit (notshown) assembled to the support and electrically connected to thenucleation conductive strips 6 _(i) by means of first connection pads 21_(i) and to the top conductive strips 14 _(j) by means of secondconnection pads 25 _(j). The control integrated circuit can compriseelectronic components such as transistors in such a way as to controlthe application of an electric potential difference, simultaneously orsequentially, to different pixels P_(ij) of diodes.

Hybridization of the control circuit to the support can be carried outby direct bonding (or molecular adhesion bonding) of the metal-metal anddielectric-dielectric type. In a variant, it can be carried out by meansof intermediate connection elements made of a meltable conductivematerial, such as indium balls, which come into contact with thedifferent first and second connection pads of the optoelectronic device1. In a variant, the control circuit can be connected to the first andsecond connection pads 21 _(i) and 25 _(j) by means of welded electricalwires (wire bonding), particularly when the connection pads are locatedon the front surface 3 b of the support.

During operation, when a first electrical potential V1 _(i) is appliedto the nucleation conductive strip 6 _(i) and a second electricalpotential V2 _(j) is applied to the top conductive strip 14 _(j), theone or more diodes 2 located in the pixel P_(ij) are activated and emitluminous radiation. The diodes 2 located in the other pixels remaindeactivated. The controlled emission of each pixel P_(ij),simultaneously or sequentially, is thus carried out by polarizing one orthe other of the nucleation conductive strips 6 _(i) and one or theother of the top conductive strips 14 _(j).

Thus, the optoelectronic device 1 comprises a plurality of diodes 2distributed in a matrix of pixels that can be activated independently ofone another by means of the first and second polarization electrodes,which are in the form of conductive strips distinct from each other.Moreover, the fact that the first polarization electrodes have asupplementary nucleation surface function makes it possible to simplifyboth the structure and the method of implementation. Each pixel can alsocomprise a developed surface area of the active zone that issubstantially equal to or greater than the surface area, in the plane(X, Y), of the pixel, such that the maximum luminous emission intensityof the optoelectronic device 1 can be greater than that of theoptoelectronic device 1 of the prior art mentioned above. One thusobtains an optoelectronic device 1 with high luminous intensity and highresolution.

According to a preferred embodiment, the optical and/or electronicproperties of the diodes 2 have improved homogeneity from one diode tothe other. For this purpose, the substrate 4 comprises a top surface 4 bformed by a monocrystalline material; the bottom insulating layer 5 ismade of a crystalline material epitaxially grown from the top surface 4b of the substrate 4; and the nucleation conductive strips 6 _(i) aremade of a material comprising a transition metal epitaxially grown fromthe crystalline material of the bottom insulating layer 5.

Thus, as shown in FIGS. 3A and 3B, the substrate 4 comprises amonocrystalline growth material at least at the level of the top surface4 b. Thus, at the level of this top surface 4 b, the growth material iscomposed of a single crystal and therefore does not comprise severalcrystals separated from one another by grain boundaries. The material ofthe substrate 4 has crystallographic properties, in terms of latticeparameter and structural type, suitable for the epitaxial growth of acrystalline material of the bottom insulating layer 5. Thus, itpreferably has a crystalline structure of the face-centered cubic typeoriented in the direction [111] or a crystalline structure of thehexagonal type oriented in the direction [0001]. Also preferably, it hasa lattice parameter a_(s) such that the lattice mismatch m=Δa/a_(s) withthe material of the bottom insulating layer 5 is less than or equal to20%. Preferably, the material of the substrate 4 is monocrystallinesilicon with a crystalline structure of the face-centered cubic type inwhich the growth plane is oriented in the direction [111] and in whichthe lattice parameter a_(s) is approximately 3.84 Å.

The bottom insulating layer 5 is made of a crystalline materialepitaxially grown from the top surface 4 b of the substrate 4. Thus, thematerial of the bottom insulating layer 5 comprises a crystal lattice inepitaxial relation to that of the monocrystalline material of thesubstrate. The crystal lattice of the material of the bottom insulatinglayer 5 has a unit cell defined in particular by its crystallographicaxes, designated here solely for illustrative purposes a_(i), b_(i),c_(i). The crystal lattice therefore has an alignment, of at least onecrystallographic axis a_(i), b_(i) oriented in the plane of the materialand of at least one crystallographic axis C_(i) oriented orthogonal tothe plane of the material, with the crystallographic axes a_(s), b_(s)and c_(s) of the monocrystalline material of the substrate respectively.This is reflected by the fact that the crystallographic axis a_(i) issubstantially parallel, at every point of the top surface 5 b, to thecrystallographic axis a_(s), as are, respectively, the crystallographicaxes b_(i) and c_(i) relative to the crystallographic axes b_(s) andc_(s). Moreover, whether the material of the bottom insulating layer 5is monocrystalline or polycrystalline, because of its epitaxial relationwith the monocrystalline material of the substrate, eachcrystallographic axis a_(i), b_(i), c_(i) is substantially identical atevery point of the top surface 5 b. In other words, the crystallographicaxes a_(i) are substantially identical, i.e. parallel to each other, atevery point of the top surface 5 b, as are, respectively, thecrystallographic axes b_(i) and c_(i). A polycrystalline material iscomposed, in contrast to a monocrystalline material, of several crystalsseparated from one another by grain boundaries.

The material of the bottom insulating layer 5 has crystallographicproperties, in terms of lattice parameter and type of crystallinestructure, such that it is suitable for being epitaxially grown from themonocrystalline material of the substrate 4. Moreover, it is suitablefor allowing the epitaxial growth of the nucleation conductive strips 6_(i) made of a material comprising a transition metal from the topsurface 5 b. It preferably has a lattice parameter such that the latticemismatch with the monocrystalline material of the substrate 4 is lessthan or equal to 20%. Moreover, the type of the crystalline structure issuch that its crystallographic axes a_(i), b_(i), c_(i) can berespectively parallel to the axes a_(s), b_(s) c_(s) of themonocrystalline material of the substrate. The crystalline structure canbe of the face-centered cubic type, oriented in the direction [111], orof the hexagonal type oriented in the direction [0001], or even of theorthorhombic type oriented in the direction [111]. Preferably, thematerial of the bottom insulating layer 5 is aluminum nitride AlN, witha lattice parameter of approximately 3.11 Å and a crystalline structureof the hexagonal type with the growth plane oriented in the direction[0001].

The nucleation conductive strips 6 _(i) are made of a materialcomprising a transition metal epitaxially grown from the top surface 5 bof the bottom insulating layer 5. The nucleation material comprises acrystal lattice that is in epitaxial relation with that of the materialof the bottom insulating layer 5. The crystal lattice of the nucleationmaterial has a unit cell defined in particular by its crystallographicaxes, designated here solely by way of example a_(n), b_(n), c_(n). Thecrystal lattice therefore has an alignment, of at least onecrystallographic axis a_(n), b_(n) oriented in the plane of the materialand of at least one crystallographic axis c_(n) oriented orthogonal tothe plane of the material, with the crystallographic axes a_(i), b_(i),and c_(i), of the material of the bottom insulating layer 5,respectively, at the level of the top surface 5 b. This is reflected bythe fact that the crystallographic axis a_(n) is substantially parallel,at every point of the nucleation surface 6 b, to the crystallographicaxis a_(i) of the top surface 5 b, as are the crystallographic axesb_(n) and c_(n) relative to the crystallographic axes b_(i) and c_(i).Moreover, whether the nucleation material is monocrystalline orpolycrystalline, each crystallographic axis a_(n), b_(n), c_(n) isidentical at every point of the nucleation surface 6 b. In other words,the crystallographic axes a_(n) are identical, i.e. parallel to eachother, at every point of the nucleation surface 6 b, as are thecrystallographic axes b_(n) and c_(n) respectively.

The nucleation material has crystallographic properties, in terms oflattice parameter and structural type, such that it can be epitaxiallygrown from the material of the bottom insulating layer 5. It is alsosuitable for the epitaxial growth from the nucleation surface 6 b of awire 9. Preferably, it thus has a lattice parameter such that thelattice mismatch with the material of the bottom insulating layer 5 isless than or equal to 20%. Moreover, the type of the crystallinestructure is such that its crystallographic axes a_(n), b_(n), c_(n) canbe respectively parallel to the axes a_(i), b_(i), c_(i) of the materialof the bottom insulating layer 5. The crystalline structure can be ofthe face-centered cubic type, oriented in the direction [111], or of thehexagonal type, oriented in the direction [0001], or even of theorthorhombic type, oriented in the direction [111]. The nucleationmaterial comprises a transition metal, i.e. it can be composed of atransition metal or a component comprising a transition metal, forexample a nitride or a carbide of a transition metal. The transitionmetals, as well as their nitrides and carbides, have in particular theadvantage of favorable electrical conductivity, close to that of themetals. The nucleation material can be selected from titanium Ti,zirconium Zr, hafnium Hf, vanadium V, niobium Nb, tantalum Ta, chromiumCr, molybdenum Mo, and tungsten W, a nitride of these elements TiN, ZrN,HfN, VN, NbN, TaN, CrN, MoN, or WN, or a carbide of these elements TiC,ZrC, HfC, VC, NbC, TaC, CrC, MoC, WC. The nitrides and carbides oftransition metals can comprise an atomic proportion of transition metalother than 50%. Preferably, the nucleation material is selected from anitride of titanium TiN, zirconium ZrN, hafnium HfN, vanadium VN,niobium NbN, tantalum TaN, chromium CrN, molybdenum MoN, or tungsten WN,or a carbide of titanium TiN, zirconium ZrN, hafnium HfN, vanadium VN,niobium NbN, or tantalum TaN. Preferably, the nucleation material isselected from a nitride or a carbide of titanium TiN, TiC, zirconiumZrN, ZrC, hafnium HfN, HfC, vanadium VN, VC, niobium NbN, NbC, ortantalum TaN, TaC. Preferably, the nucleation material is selected froma nitride of titanium TiN, zirconium ZrN, hafnium HfN, niobium NbN, ortantalum TaN. Preferably, the nucleation material is selected from anitride of hafnium HfN or niobium NbN.

The first doped regions 9 of the diodes 2 are epitaxially grown from thenucleation surfaces 6 b of the different nucleation conductive strips 6_(i). The material of the wire comprises a crystal lattice that is inepitaxial relation with that of the nucleation material. The crystallattice of the material of the wire has a unit cell defined inparticular by its crystallographic axes, designated here solely by wayof example a_(f), b_(f), c_(f). The crystallographic axes a_(f), b_(f),c_(f) of the material of the wire are respectively substantiallyparallel to the crystallographic axes a_(n), b_(n), c_(n) of thenucleation material at the level of the nucleation surface 6 b. In otherwords, the crystallographic axis a_(f) is parallel to thecrystallographic axis a_(n) of the nucleation surface 6 b. The sameapplies for the crystallographic axes b_(f) and c_(f) relative to thecrystallographic axes b_(n) and c_(n). Moreover, provided that thecrystallographic axes a_(n), b_(n), c_(n) are respectively identicalfrom one nucleation surface 6 b, to the other, each crystallographicaxis a_(f), b_(f), c_(f) is identical from one wire 9 to the other. Inother words, the crystallographic axes a_(f) are identical, i.e.parallel to each other, from one wire to the other. The same applies forthe crystallographic axes b_(n) and c_(n). Thus, the wires havecrystallographic properties, in terms of orientation and position of thecrystal lattice, that are substantially identical. The optoelectronicdevice 1 thus has crystallographic properties that are substantiallyhomogenous at the level of the wires, which contributes toward makingthe electrical and/or optical properties of the electroluminescentdiodes 2 homogeneous.

The inventors thus found that, surprisingly, the nucleation regionscomposed of transition metal nitride are epitaxially grown and notmerely textured when they are deposited on a bottom insulating layer 5that is grown epitaxially and not directly from the top surface 4 b ofthe monocrystalline material of the substrate.

The term epitaxy is understood as meaning that the crystalline epitaxialmaterial comprises a crystal lattice or crystalline structure that is inepitaxial relation with that of the nucleation material from which it isepitaxially grown. The term epitaxial relation is understood to meanthat the epitaxial material has an alignment of the crystallographicorientations of its crystal lattice, in at least one direction in theplane of the material and at least one direction orthogonal to the planeof the material, with those of the crystal lattice of the nucleationmaterial. Here, the plane of the epitaxial material is a growth plane ofthe material parallel to the nucleation surface. The alignment ispreferably carried out to within 30°, or even within 10°. This isreflected by the fact that there is a total match of orientation andcrystallographic position between the crystal lattice of the epitaxialmaterial and that of the nucleation material. Preferably, thecrystalline epitaxial material has a lattice parameter a₂, measured inthe growth plane, such that the lattice mismatch m=(a₂−a₁)/a₁=Δa/a₁ withthe nucleation material of lattice parameter a₁ is less than or equal to20%. Thus, when a crystalline material is epitaxially grown from acrystalline nucleation material, i.e. formed by epitaxial growth, theepitaxial relation between these two crystalline materials is reflectedby the fact that at least one crystallographic axis of the crystallattice of the epitaxial material, oriented in the plane of theepitaxial material, for example a_(e) and/or b_(e), and at least onecrystallographic axis, oriented orthogonal to the plane, for examplec_(e), are respectively substantially parallel to the crystallographicaxes a_(n) and/or b_(n) and c_(n) of the crystal lattice of thenucleation material.

An epitaxial material is a particular case of so-called texturedmaterials, in the sense that textured materials have a preferentialcrystallographic direction oriented orthogonal to the plane of thematerial, but do not have a preferential crystallographic directionoriented in the plane of the material. In addition, the preferentialcrystallographic direction orthogonal to the plane of the texturedmaterial is not or is only minimally dependent on the crystallineproperties of the nucleation material. Thus, a textured material has asingle preferred crystallographic direction, for example that of the caxis, and not three preferred directions. The network of the texturedmaterial thus has a polycrystalline structure of which the differentcrystalline domains, separated by grain boundaries, are all orientedalong the same preferred crystallographic c axis. In contrast, they donot have relations of parallelism among them in the growth plane. Inother words, the c axes of the crystalline domains are parallel to eachother, but the a axes, like the b axes, are not parallel to each otherand are oriented in a substantially random manner. This preferredcrystallographic direction is not or is only minimally dependent on thecrystalline properties of the nucleation material. Thus, it is possibleto obtain a textured material from a nucleation material having amonocrystalline, polycrystalline, or even amorphous structure.

Thus, as shown in FIG. 3C, the wires 9, here made of GaN epitaxiallygrown by MOCVD, when they are epitaxially grown from a nucleationmaterial that is textured and not epitaxially grown, all have the samegrowth direction, the latter being substantially parallel to thecrystallographic axis c_(n). In contrast, it can be seen that thehexagonal shape of the wires 9 is not oriented in an identical mannerfrom one wire to the other, which reflects the fact that thecrystallographic axes a_(f) and b_(f) are not respectively oriented inan identical manner from one wire to the other. The wires 9 then havecrystallographic properties that differ from one wire to the other,which can be reflected in a certain degree of heterogeneity in theelectrical and/or optical properties of the electroluminescent diodes 2.

In contrast, as shown in FIG. 3D, the wires 9, here made of GaNepitaxially grown by MOCVD, when they are epitaxially grown from anucleation epitaxial material and not textured, all have the same growthdirection, the latter being substantially parallel to thecrystallographic axis c_(n). Moreover, it can be seen that the hexagonalshape of the wires 9 is oriented here in an identical manner for all ofthe wires 9, which reflects the fact that the crystallographic axesa_(f) and b_(f) are respectively oriented in an identical manner fromone wire to the other. Thus, the wires 9 have crystallographicproperties, in terms of orientation and crystal lattice position, thatare substantially identical. The optoelectronic device 1 thus hascrystallographic properties that are substantially homogeneous at thelevel of the wires 9, which contributes toward making the electricaland/or optical properties of the electroluminescent diodes 2homogeneous.

FIGS. 4A to 4I show a schematic and partial cross-sectional view ofvarious steps of an example of a production method of the optoelectronicdevice 1 according to the preferred embodiment described above. Eachfigure shows a sectional view along plane AA (left) and a sectional viewalong plane BB (right).

Referring to FIG. 4A, the substrate 4 composed of a monocrystallinematerial is provided at least at the level of the top surface. In thisexample, the substrate 4 is made of silicon having a structure of theface-centered cubic type oriented in the direction [111]. Its latticeparameter in the plane of the top surface is of the order of 3.84 Å.

After this, one disposes the bottom insulating layer 5 in such a way asto cover the top surface of the substrate by means of a method of thechemical vapor deposition (CVD) type, for example with organometallicprecursors (MOCVD, metal-organic chemical vapor deposition) or by amethod of the molecular beam epitaxy (MBE) type, the hybrid vapor phaseepitaxy (HVPE) type, the atomic layer epitaxy (ALE) type or atomic layerdeposition (ALD) type, or even by evaporation or sputtering.

In this example, the material of the bottom insulating layer 5 isepitaxially grown aluminum nitride, the crystalline structure of whichis of the hexagonal type and is oriented in the direction [0001]. Itslattice parameter in the plane (X, Y) is of the order of 3.11 Å. It isdeposited by MOCVD. The nominal V/III ratio, defined as the ratio of themolar flux of group V elements to the molar flux of group III elements,i.e. here the N/Al ratio, is between 200 and 1000. The pressure is ofthe order of 75 torr. The growth temperature T, measured at the level ofthe substrate, can in a first stage be greater than or equal to 750° C.for the nucleation phase, and in a second stage be of the order of 950°C. for the growth phase.

Referring to FIG. 4B, one forms the nucleation conductive strips 6 _(i)on the top surface of the bottom insulating layer 5. For this purpose,one carries out epitaxial growth of a layer of a nucleation materialcomprising a transition metal, for example by means of a sputteringtechnique, in which the growth temperature is advantageously betweenroom temperature, for example 20° C., and 1000° C. Surprisingly, thenucleation strips are also epitaxially grown when they are deposited bysputtering at a growth temperature between room temperature, for example20° C., and 500° C., for example a temperature substantially equal to400° C. The power can be of the order of 400 W. The pressure can be ofthe order of 8.10⁻³ torr. The techniques of high-temperature sputteringand chemical vapor deposition can also be used. After this, by means ofclassical photolithography and etching techniques, the continuous layerof the nucleation material is etched to form a plurality of nucleationconductive strips 6 _(i) that are distinct from one another.

Advantageously, in cases where the nucleation conductive strips 6 _(i)are made of a polycrystalline material, a crystallization annealing stepcan be carried out in such a way as to obtain a monocrystallinenucleation material. The annealing can be carried out at an annealingtemperature substantially corresponding to the crystallizationtemperature of the nucleation material, namely 1620° C. in the presentcase of a transition metal nitride. Surprisingly, however,crystallization of the nucleation material can also be obtained at anannealing temperature less than the crystallization temperature, forexample in a temperature range of 600° C. to 1620° C., and preferablybetween 800° C. to 1200° C., for example equal to approximately 1000° C.The annealing can be carried out for a period for example of greaterthan 1 min, preferably greater than 5 min, or even than 10 min, forexample 20 min. It can be carried out under a flow of nitrogen (N₂) andammonia (NH₃). The pressure can be of the order of 75 torr.

Referring to FIG. 4C, one then deposits the intermediate insulatinglayer 7, forming a growth mask, and produces the through-openings 8. Alayer of a dielectric material is thus deposited in such a way as tocover the nucleation conductive strips 6 _(i) and the bottom insulatinglayer 5, and through-openings 8 are then formed in such a way as to openlocally onto the nucleation surfaces. The dielectric material is e.g. anoxide of silicon (such as SiO₂) or a nitride of silicon (such as Si₃N₄),or even a stack of several different dielectric materials. It is etchedin a selective manner with respect to the material of the nucleationconductive strips 6 _(i). Preferably, the lateral dimensions of theopenings are less than the width of the nucleation conductive strips 6_(i), for example at least two times less.

Referring to FIG. 4D, the wires 9, here made of GaN, are formed byepitaxial growth from the nucleation surfaces of the differentnucleation conductive strips 6 _(i), through the openings of theintermediate insulating layer 7, for example according to a methodidentical or similar to that described in the document WO2012/136665.The growth temperature is increased to a first value T₁, for examplebetween 950° C. and 1100° C., and particularly between 990° C. and 1060°C. The nominal V/III ratio, here the N/Ga ratio, has a first value(V/III)₁ of approximately 10 to 100, for example substantially equal to30. The group III and group V elements are derived from precursorsinjected into the epitaxy reactor, for example trimethylgallium (TMGa)or triethylgallium (TEGa) for gallium, and ammonia (NH₃) for nitrogen.The H₂/N₂ ratio has a first value (H₂/N₂)₁ greater than or equal to60/40, and preferably greater than or equal to 70/30, or even more, forexample substantially equal to 90/10. The pressure can be fixed atapproximately 100 mbar. One thus obtains first doped regions 9 in theform of wires that extend along the longitudinal axis Δ from thenucleation surfaces. The first semiconductor compound of the first dopedregions 9, namely GaN in this case, is n-doped with silicon. The bottomportion 12 of the wires 9 is located in the openings of the intermediateinsulating layer 7, and is prolonged along the longitudinal axis Δ bythe top portion 13. One obtains here a plurality of wires 9 epitaxiallygrown from the nucleation surfaces, the crystallographic properties ofwhich are substantially identical, provided that nucleation of the wires9 has been carried out from nucleation surfaces that have substantiallythe same crystallographic properties.

The active zones are formed by epitaxial growth from the exposed surfaceof the wires 9, i.e. here on the top portion 13 of the wires 9. Morespecifically, one forms a stack of barrier layers and at least one layerthat forms a quantum well, said layers being alternated in the directionof the epitaxial growth. The layers that form the quantum wells and thebarrier layers can be made of InGaN, with different atomic proportionsfor the layers of quantum wells and the barrier layers. By way ofexample, the barrier layers are made of In_(x)Ga(_(1-x))N, where x isapproximately equal to an atomic proportion of 18%, and the layers ofquantum wells are also made of In_(y)Ga(_(1-y))N, where y is greaterthan x, for example of the order of an atomic proportion of 25%, in sucha way as to improve the quantum confinement of the charge carriers inthe quantum wells. The formation of the barrier layers and the layers ofquantum wells can be carried out at a growth temperature value T₃substantially equal to the value T₂, namely here 750° C. The V/III ratiohas a value (V/III)₃ substantially equal to the value (V/III)₂. TheH₂/N₂ ratio has a value substantially equal to the value (H₂/N₂)₂ duringthe formation of the barrier layers and has a value substantially lessthan the value (Hz/N₂)₂ during the formation of the layers of quantumwells, for example 1/99. The pressure can remain unchanged. One thusobtains barrier layers of InGaN with an atomic proportion ofapproximately 18% indium and layers of quantum wells of InGaN with anatomic proportion of approximately 25% indium.

The second p-doped regions are then formed by epitaxial growth in such away as to cover and at least partly surround the active zones. For thispurpose, the growth temperature can be raised to a fourth value T₄greater than the value T₃, for example of the order of 885° C. The V/IIIratio can be increased to a fourth value (V/III)₄ greater than the value(V/III)₃, for example of the order of 4000. The H₂/N₂ ratio is increasedto a fourth value (H₂/N₂)₄ greater than the value (H₂/N₂)₂, for exampleof the order of 15/85. Finally, the pressure can be reduced to a valueof the order of 300 mbar. One thus obtains second p-doped regions 11,composed for example of GaN or InGaN of the p-doped type, that cover andhere continuously surround the active zones. The second p-doped regions11 and the active zones thus form the shells of the diodes 2 in acore/shell configuration. In this example, the active zone and thesecond doped region 11 of the diodes 2 cover the top portion 13 of eachwire from the top surface of the intermediate insulating layer 7.

Referring to FIG. 4E, the top conductive strips 14 _(j) are formeddistinct from each other, extending on the top surface of theintermediate insulating layer 7 and coming into contact with the seconddoped regions 11 of the diodes. For this purpose, a continuous layer ofa conductive material, here partially transparent to the luminousradiation emitted by the diodes, is conformally disposed. After this, bymeans of photolithography and etching, the top conductive strips 14 _(j)are formed so as to be distinct from each other. Here, each stripcomprises portions that cover the second doped regions 11 of a set D_(j)of diodes, these covering portions 15 _(j) being connected two by two byconnecting parts 16 _(j) that extend on the top surface of theintermediate insulating layer 7.

Referring to FIG. 4F, advantageously, the connecting parts 16 _(j) ofthe top conductive strips 14 _(j) are covered by a metal layer 17suitable for reducing the electrical resistance of the top conductivestrips 14 _(j) and thus improving circulation of the electric current.This metal layer 17 is deposited on the top conductive strips 14 _(j)and is then etched so as to cover only the connecting parts 16 _(j) andnot the covering portions 15 _(j). This metal layer 17 can be composedof one or more materials selected from aluminum, silver, gold, or anyother suitable material, and has a thickness for example of between 5 nmand 200 nm, and preferably between 10 nm and 100 nm, for example equalto approximately 30 nm. In a variant, the metal layer 17 can bedeposited prior to deposition of the top conductive strips 14 _(j). Itis etched in such a way as not to extend around the second doped regions11 along the Z axis.

Referring to FIG. 4G, advantageously, one disposes the top insulatinglayer 18 in such a way as to continuously cover the top conductivestrips 14 _(j), the metal layer 17 and the intermediate insulating layer7. The top insulating layer 18 is made of a dielectric material such ase.g. an oxide of silicon (such as SiO₂) or a nitride of silicon (such asSi₃N₄), or even a stack of several different dielectric materials.

Referring to FIG. 4H, advantageously, one then disposes a reflectinglayer 19 in such a way as to cover the surface of the top insulatinglayer 18 without covering the wires 9. The reflecting layer 19 thusextends essentially in the plane (X, Y). This reflecting layer 19 can becomposed of one or more materials selected from aluminum, silver, gold,or any other suitable material and has a thickness for example ofbetween 20 nm and 1500 nm, preferably between 400 nm and 800 nm. Thethickness of the reflecting layer 19 is selected such that the incidentluminous radiation emitted by the diodes 2 is reflected in the direction+Z.

Referring to FIG. 4I, one disposes an encapsulation layer 20 in such away as to entirely cover the diodes. The encapsulation layer 20 is madeof a dielectric material transparent to the luminous radiation emittedby the diodes 2, such as e.g. an oxide of silicon (such as SiO₂) or anitride of silicon (such as Si₃N₄), or even a stack of several differentdielectric materials. The thickness of the encapsulation layer 20 is forexample between 250 nm and 50 μm.

The first 21 _(i) and second 25 _(j) connection pads are then produced.In cases where these pads are made on the rear surface 3 a of thesupport, the substrate 4 is thinned, and the first through openings 22_(i), which open onto the nucleation conductive strips 6 _(i), and thesecond through openings 26 _(j), which open onto the top conductivestrips 14 _(j), are then made. The sides of the through openings can becoated with an insulating layer 24, then a conductive material 23 fillsthe interior of the through openings. The first and second connectionpads 21 _(i) and 25 _(j) are then formed respectively at the level ofeach first and second through opening 22 _(i) and 26 _(j). Hybridizationof the support to a control integrated circuit is then carried out bymolecular bonding, wire cabling, or connection by means of conductiveand meltable elements.

The production method of the optoelectronic device 1 has the advantageof not requiring individual electrical separation of the diodes 2 bymeans of insulating trenches formed between the diodes 2 from the frontsurface 3 b of the support. The diodes 2 are here individually separatedby the first and second electrodes that are in the form of conductivestrips distinct from each other. Thus, the support has improvedmechanical strength, which in particular facilitates hybridization tothe control circuit. Moreover, the diodes 2 have retained optical and/orelectronic properties, provided that individual separation of the diodes2 does not require, as in the example of the prior art mentioned above,etching of the doped regions and the active zone. The homogeneity of theoptical and/or electronic properties of the diodes 2 is also improvedwhen the diodes 2 are formed from nucleation conductive strips 6 _(i) inepitaxial relation with the monocrystalline material of the substrate.

Particular embodiments have just been described. Different variants andmodifications will be obvious to the person skilled in the art.

Thus, as shown in FIG. 5, each pixel P_(ij) can comprise several diodes.Thus, application of a potential difference to the pixel P_(ij) resultsin activation of the diodes 2 of this pixel, the diodes 2 of the otherpixels remaining deactivated.

In addition, as shown in FIG. 6A, the optoelectronic device 1 cancomprise a routing integrated circuit 28 with electricalinterconnections 29 providing connection in series of several pixelsamong one another. In this example, the diodes 2 of the pixel P₁ areconnected in series with the diodes 2 of the pixel P₂ by means of theelectrical interconnections 29 of the routing circuit 28 connected tothe first and second through openings 22 _(i), 26 _(j). The routingintegrated circuit 28 can be assembled and electrically connected to thecontrol circuit (not shown) by means of the connection pads 21 _(i), 25_(j). Thus, in this example, a potential difference can be applied tothe pixels P₁ and P₂ connected in series by means of connection pads 21₂ and 25 ₁. The electrical potential of the connection pad 25 ₁ isapplied to the top conductive strip 14 ₁ of the pixel P₁ by means of thethrough opening 26 ₁ and the interconnexion 29.1, and the electricalpotential of the connection pad 21 ₂ is applied to the nucleationconductive strip 6 ₂ of the pixel P₂ by means of the through opening 22₂ and the interconnexion 29.3. The pixels P₁ and P₂ are connected inseries by the electrical connection of the nucleation conductive strip 6₁ of the pixel P₁ with the top conductive strip 14 ₂ of the pixel P₂carried out by means of the through openings 22 ₁ and 26 ₂ and theinterconnexion 29.2. In a variant, the interconnexion 29.2 can beomitted and the through openings 22 ₁ and 26 ₂ can be in directelectrical contact in the substrate 4.

As shown in FIG. 6B, the optoelectronic device 1 can comprise one orseveral electrical interconnections 30 located at the level of theintermediate insulating layer 7, which allows, in this example, theserial connection of the diodes 2 of the pixel P₁ with the diodes 2 ofthe pixel P₂. The electrical interconnection 30 is formed here by athrough opening filled with a conductive material opening on the onehand onto the nucleation conductive strip 6 ₁ of the pixel P₁ and on theother onto the top conductive strip 142 of the pixel P₂. In thisexample, a routing circuit 28 is provided which provides electricalpolarization of the pixels P₁ and P₂ connected in series by means of theinterconnexions 29.1 and 29.3.

The examples of FIGS. 6A and 6B are given solely by way of example, andother configurations of electrical interconnections that are internal orformed in a routed integrated circuit are possible so as to provide aconnection of the pixels either in series or in parallel. In addition,in a variant, and as mentioned above, the electrical connection pads canbe located on the front surface or the rear surface of the support.

Thus, we have described an optoelectronic device 1 comprisingelectroluminescent diodes 2 that can advantageously form a displayscreen or an image projector of high luminous intensity and high spatialresolution. However, the invention also applies to the field ofphotodiodes suitable for receiving and detecting luminous radiation andconverting it into electrical signals relative to the various pixels.

We have described three-dimensional diodes 2 of the wire type, but theinvention also applies to the first doped regions in the form ofthree-dimensional pads of which the height along the Z axis is of thesame order of magnitude as their transverse dimensions in the plane (X,Y), and to the first doped regions in the form of optionally truncatedpyramids.

We have described diodes 2 in a core/shell configuration wherein theactive zones and the second doped regions cover the sides and the peakof the wires 9. The invention also applies to the axial configuration ofthe diodes 2 wherein the active zones and the second doped regions coveronly the peak of the wires.

We have also described a relative orientation substantially orthogonalto the nucleation conductive strips with respect to the top conductivestrips, but other orientations are possible wherein the nucleationstrips and the top strips form for example, two by two, a non-zero angleof less than or greater than 90°.

1. An optoelectronic device, comprising: a support including a rearsurface and a front surface opposite each other; a plurality ofnucleation conductive strips forming first polarization electrodes,distinct from each other and resting on the front surface, made of anelectrically conductive material configured for the growth of firstdoped regions of diodes; an intermediate insulating layer covering thenucleation conductive strips, and including through-openings openingonto the nucleation conductive strips; a plurality of diodes, each ofthe plurality of diodes including a first three-dimensional doped regionand a second doped region disposed to form a p-n junction, the firstdoped regions being in contact with the nucleation conductive stripsthrough the through-openings and extending along a longitudinal axissubstantially orthogonal to the front surface; and a plurality of topconductive strips forming second polarization electrodes, distinct fromeach other and resting on the intermediate insulating layer, each topconductive strip being disposed to be in contact with second dopedregions of a set of diodes of which the first doped regions are incontact with different nucleation conductive strips.
 2. Theoptoelectronic device as claimed in claim 1, wherein the supportincludes an electrically insulating substrate, a top surface of theelectrically insulating substrate forming the front surface, or includesa semiconductor or electrically conductive layer or substrate coatedwith a bottom insulating layer, one surface of which forms the frontsurface.
 3. The optoelectronic device as claimed in claim 1, whereineach nucleation conductive strip extends longitudinally on the frontsurface and is electrically separated from its neighbors, transversely,by the intermediate insulating layer.
 4. The optoelectronic device asclaimed in claim 1, wherein each top conductive strip extendslongitudinally on the intermediate insulating layer, and is electricallyseparated from its neighbors, transversely, by a top insulating layer.5. The optoelectronic device as claimed in claim 1, wherein the topconductive strips are made of an at least partially transparentconductive material and at least partially cover the second dopedregions.
 6. The optoelectronic device as claimed in claim 5, whereineach top conductive strip includes portions covering the second dopedregions of a set of diodes, the covering portions being connected toeach other by connecting parts resting on the intermediate insulatinglayer.
 7. The optoelectronic device as claimed in claim 6, wherein theconnecting parts of the top conductive strips are at least partiallycoated with a metal layer.
 8. The optoelectronic device as claimed inclaim 1, further comprising: at least one of first connection pads andsecond connection pads, the first connection pads resting on the rearsurface and electrically connected to the nucleation conductive stripsby first openings passing through the support and filled with aconductive material, and the second connection pads resting on the rearsurface and electrically connected to the top conductive strips bysecond openings passing through the support and the intermediateinsulating layer and filled with a conductive material.
 9. Theoptoelectronic device as claimed in claim 1, further comprising: acontrol integrated circuit assembled to the support and electricallyconnected to the nucleation conductive strips and the top conductivestrips, configured to apply a potential difference, sequentially, todifferent subsets of diodes, the one or more diodes of a same subsetbeing in contact with a same nucleation conductive strip and a same topconductive strip, the one or more diodes of different subsets of diodesbeing in contact with at least one of different nucleation conductivestrips and different top conductive strips.
 10. The optoelectronicdevice as claimed in claim 1, wherein at least one diode in contact witha first nucleation conductive strip and a first top conductive strip isconnected in series with at least one other diode, the latter being incontact with a second nucleation conductive strip distinct from thefirst nucleation strip and a second top conductive strip distinct fromthe first top strip.
 11. The optoelectronic device as claimed in claim1, wherein the support includes a substrate made of a monocrystallinematerial that forms a top surface, on which rests a bottom insulatinglayer made of a dielectric material epitaxially grown from the topsurface of the substrate and forming an opposing top surface, thenucleation conductive strips being made of a material comprising atransition metal forming a crystalline nucleation material, epitaxiallygrown from the top surface of the bottom insulating layer and forming anucleation surface on which the first doped regions of the diodes are incontact.
 12. The optoelectronic device as claimed in claim 11, whereinthe material of the bottom insulating layer is selected from aluminumnitride and oxides of aluminum, titanium, hafnium, magnesium andzirconium, and has a hexagonal, face-centered cubic, or orthorhombiccrystalline structure.
 13. The optoelectronic device as claimed in claim11, wherein the material of the nucleation conductive strips is selectedfrom titanium, vanadium, chromium, zirconium, niobium, molybdenum,hafnium, tantalum and tungsten, or from a nitride or a carbide oftitanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium,tantalum and tungsten, and has a hexagonal or face-centered cubiccrystalline structure, or is a gallium-nitride-based material.
 14. Theoptoelectronic device as claimed in claim 11, wherein themonocrystalline material of the substrate is selected from a group III-Vcompound, a group II-VI compound, or a group IV element or compound andhas a hexagonal or face-centered cubic crystalline structure.
 15. Amethod for producing the optoelectronic device as claimed in claim 1,comprising: epitaxial growing of the nucleation conductive strips bysputtering at a growth temperature between room temperature and 500° C.